Ice dam risk in Lewiston, ME
Will your roof get ice dams in Lewiston, ME?
33.3 dam days a winter
High risk. On an ordinary house in Lewiston, conditions for an ice dam come on about 33.3 days in a normal winter, mostly in January and February.
Lewiston averages 65 inches of snow a year and about 107 days with snow on the ground. Snow that lies that long is what turns a little attic heat into a ridge of ice at the eave. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
What your attic does to that number in Lewiston
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 17.0 | High |
| Typical, some insulation, not air-sealed | 33.3 | High |
| Older or poorly insulated, warm attic | 53.6 | Severe |
Sealing and insulating a typical attic takes out about 16.3 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 53.6 days.
What to do about ice dams in Lewiston
- Air-seal the attic floor: the gaps around the hatch, light fixtures, plumbing stacks and the top plates of interior walls. This is the fix that removes the cause, and it usually costs less than a season of contractor ice removal.
- Rake the bottom three or four feet of roof after any storm that leaves more than about six inches, from the ground with a roof rake.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
- Heat cable is worth pricing here even on a sealed house, along the eave and in the gutters and downspouts it drains into.
Running 60 feet of 5 W/ft cable whenever snow lies below freezing would use about 293 kWh a winter in Lewiston, roughly $50 at 17 cents a kWh.
Which to spend on first: air sealing or heat cable.
Lewiston winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 19.4 | 28.7 | 11.0 |
| February | 17.3 | 27.4 | 9.7 |
| March | 12.3 | 23.4 | 5.8 |
| April | 2.9 | 5.6 | 0.5 |
| November | 1.6 | 2.9 | 0.5 |
| December | 11.6 | 18.9 | 5.9 |
Lewiston next to nearby towns
Lewiston ranks 2 of 11 Maine cities here for ice-dam days, behind Waterville at 40.9 days.
- Auburn, ME 4 mi, 31.3 days
- Augusta, ME 28 mi, 30.3 days
- Westbrook, ME 28 mi, 22.4 days
- Portland, ME 32 mi, 22.4 days
- South Portland, ME 32 mi, 22.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Lewiston, 2.3 miles from Lewiston. A dam day is a day with snow on the roof and freezing at the eave while heat or sun melts the snow above it. This describes a normal winter, not this one.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.